1. Field
The present disclosure relates to a temperature detecting circuit.
2. Description of the Related Art
Hydrogen, which is used as a fuel for a fuel cell, is filled into a high pressure gas tank (also simply referred to as tank) for a fuel cell installed in an automobile, in a state in which the hydrogen is compressed to a high pressure of several tens MPa. There are cases in which, when filling the tank with hydrogen as mentioned above, the temperature inside the tank rises abruptly, and when the automobile is running, the hydrogen inside the tank is released from the tank, causing an abrupt drop in temperature. Such temperature rise and temperature drop make it a challenge to keep and control the tank temperature within a range that is determined by a statutory upper limit on the tank temperature, and a lower limit temperature required for maintaining sealability. Accordingly, it is necessary to control the temperature inside the tank to an appropriate temperature. To this end, it is necessary to detect the temperature that fluctuates widely from high to low inside the tank.
A thermistor disclosed in Japanese Unexamined Patent Application Publication No. 5-34208 exists as this type of technique. This thermistor is of a negative temperature coefficient (NTC) type whose resistance decreases with an increase in detected temperature. This thermistor is configured so that two or more thermistor elements that differ in B constant, which indicates the sensitivity of a thermistor with respect to temperature, are connected in parallel to a pair of lead wires. According to this configuration, favorable resistance-temperature characteristics are obtained over a wide temperature range, resulting in wide usage temperature range.
In addition, there is a thermistor with an embedded pull-up resistor disclosed in Japanese Patent No. 3365013. In this type of thermistor, a thermistor and a pull-up resistor are arranged side by side on the same substrate. In this configuration, by making the resistance of the pull-up resistor variable in accordance with detected temperature, it is possible to detect temperature with high accuracy over a wide temperature range.